United States-backed militia and the Syrian Army advanced in separate offensives against the Islamic State in eastern Syria on Saturday, piling pressure on shrinking territory the group still holds in oil-rich areas near the Iraqi border, Reuters reported.

The Syrian Democratic Forces, a US-backed alliance of Arab and Kurdish fighters, launched a new operation against the terrorist group in the north of the Deir al-Zor province. The operation aims to capture areas north and east of the Euphrates river.

“The first step is to free the eastern bank of the Euphrates and the areas Islamic State still holds,” Ahmed Abu Kholeh, head of the Deir al-Zor Military Council that is fighting as part of the SDF, told Reuters.

Meanwhile, Syrian government forces and their allies, backed by Russia and Iran, seized an oil field from militants on the other side of the Euphrates. The forces had also ended the Islamic State’s siege against provincial capital Deir el-Zour on September 5.

Crowded battlefield

The Syrian conflict started as a popular uprising against President Bashar al-Assad in 2011, but has since drawn military involvement of several world powers. Peace talks have repeatedly failed to bring an end to the war.

Saturday’s advances against the Islamic State in territory it has held for years is expected to bring the US-backed forces and the Syrian government (backed by Russia and Iran) into closer proximity in a crowded battlefield.

In June, a US warplane shot down a Syrian Army jet near Raqqa and the Syrian Democratic Forces accused the Syrian government of bombing its positions – showing the risk of escalation between the warring sides.